The present invention is directed to bicycle derailleurs and, more particularly, to a bicycle derailleur that is actuated by compressed gas.
A shift unit having a plurality of gears is used on a bicycle in order to climb hills more easily or to ride faster on flat ground. A shift unit generally has a shift control component that the rider uses to make a shift, and a shift mechanism that is linked to the shift control component by a cable.
The shift control component has, for example, two shift levers and a cable winder that rotates via a ratchet mechanism when the shift levers are operated. Shift mechanisms come in external and internal types. An external shift mechanism has a plurality of sprockets that are set up parallel to each other and that have different numbers of teeth, and a derailleur that moves back and forth in the axial direction of the sprockets (hereinafter referred to as the "shift direction") and that is used to guide the chain to one of the sprockets. The derailleur has a mounting component that is mounted to the bicycle frame, and a chain guide component that moves with respect to the mounting component and guides the chain in the shift direction. An internal shift mechanism has a plurality of transmission mechanisms of different gear ratios that are provided inside the rear wheel hub, and a controller that moves back and forth in the hub axial direction or around the hub axis and selects one of the plurality of transmission mechanisms.
With conventional shift units, operation of one of the shift levers causes the cable winder to rotate via the ratchet mechanism in one direction by one gear. As a result, the cable is wound around the cable winder, and a shift, such as from a higher to a lower gear, is made by the shift mechanism. Operation of the other shift lever causes the ratchet mechanism to be released and the cable winder to rotate in the other direction by one gear. As a result, the cable that was wound on the cable winder is played out, and a shift is made in the opposite direction by the shift mechanism.
The majority of the effort expended by the rider during riding, especially during a race, goes into pedaling. Accordingly, an important evaluation of a shift unit is how much it can reduce the effort the rider must exert to operate the shift levers. In order to reduce the effort the rider must exert to operate the shift levers, the stroke of the shift levers must be shortened and their operating force reduced. However, these two requirements are antinomic. For example, the operating force increases if the operating stroke is shortened, and the operating stroke becomes longer if the operating force is reduced. Consequently, with a system whereby a shift is made by winding a cable by means of shift levers, satisfying both of these requirements at the same time is next to impossible.
One known means for solving this problem is an external assisted shifting system that utilizes power from a battery to move the chain guide component of the derailleur. This system is disclosed in Japanese Laid-Open Patent Application 5-338581. This assisted shifting system is equipped with a conversion mechanism, a control mechanism, and an index mechanism. The conversion mechanism has cams and other such members that are provided on the inside of the chain guide component. The purpose of the conversion mechanism is to convert the rotation of the pulley and other rotating members that make up the chain guide component into displacement in the shift direction, that is, to convert rotational movement into linear reciprocal movement. The control mechanism has a control shaft linked to the conversion mechanism and moves back and forth, and a pair of electric solenoids, the rod tips of which engage with the lateral surfaces of the control shaft. This mechanism is used to control the shift direction of the chain guide component. Depressions that have inclined surfaces and perpendicular surfaces are formed on the lateral surfaces of the control shaft according to the shift position, and the positions of the inclined surfaces in the depressions are formed on opposite sides from each other on the lateral surfaces. Power is supplied from the battery to the electric solenoid via a shift operating switch mounted on the handlebar or another suitable location, and the electric solenoid is actuated by this shift operating switch. When the electric solenoid is actuated and the rod tips engage with the depressions, the control shaft and the chain guide component are engaged immovably in either of the shift directions. The index mechanism serves to hold the chain guide component in the shift position after it has been moved, with the shift direction controlled by the control mechanism. This index mechanism is provided with a complementary conductor that is used to turn off the electric solenoid when the shift direction is held.
With this assisted shifting system, when the pedals are turned, the rotating members are rotated by the chain, and this rotation causes the control shaft to move back and forth in the shift direction. When the shift operating switch is then operated, the electric solenoid is actuated according to the switch, and the rod tips of the electric solenoid engage with one set of the depressions on the lateral surfaces of the control shaft. As a result, the chain guide component, including its pulley, moves in one shift direction along with the control shaft, and is held in the shift position by the index mechanism. When the chain guide component is held by the index mechanism, the electric solenoid retracts and the shift is complete.
With this assisted shifting system, the gears can be changed by actuating the electric solenoid through operation of the switch, so the rider does not need to exert as much effort to make a shift. However, since a battery is utilized as the power source (drive source), if a dry cell or other such disposable battery is used, it must be replaced every time it is used up. Thus, ensuring an available drive source drives up the cost. On the other hand, if a nickelcadmium cell or other such rechargeable battery is used, there is less cost entailed in ensuring a drive source, but charging takes a long time, and once the cell goes dead the assisted shifting system cannot be actuated until recharging is complete. In order to keep this from happening, a number of cells must be readied, taking into account the charging time and the service life of the charged cell, and these cells must always be kept in a fully charged state, which means that battery maintenance is inconvenient.
Another problem with electrically operated devices arises when the device is used in a wet environment. If muddy water or the like adheres to the electric solenoid, the complementary conductor, or other electrical parts during use in the rain or during use in a mountain bike race, there is the danger that defective insulation may cause the electric solenoid to malfunction. The environment in which this system can be used reliably is therefore limited.
U.S. Pat. No. 4,352,503 and EPO 120,571 disclose a derailleur that operates with compressed gas. A gas pumping mechanism is operated by the rotation of the wheel during riding. The pumping mechanism operates such that high speed riding produces a high gas pressure, and low speed riding produces a low gas pressure. The gas pressure is communicated to a piston which, in turn, is connected to a derailleur operating cable. The position of the derailleur thus is determined by the gas pressure generated by the pumping mechanism.
One drawback of this type of system is that the pumping mechanism creates a drag on the wheel or other rotating part during riding, thus increasing the effort that must be exerted by the rider. Furthermore, if the rider wants to select a particular gear, the rider must intuitively learn how much gas pressure is needed to select the gear, and then the rider must concentrate on operating the desired valve for the correct amount of time until the derailleur reaches the desired gear. Such a distraction can be very troublesome during a race or during other high performance riding.